If you want to prep your tracks for a target platform and specifically a target loudness for streaming then the new FabFilter Pro L2 (available in the Auria store) is the best option by a very wide margin.

There are other options available, either is IAA, AU, or standalone. For example Grand Finale by Klevgrand, FAC Maxima, Final Touch, Audio Mastering, and Lurssen Mastering Console. These all tend towards a loud (and now out of date) CD mastering workflow but if used carefully can also achieve good results - the trick is to not push them too hard.

All modern streaming platforms (YouTube, Spotify, iTunes) normalise tracks to an average loudness of -14 LUFS, so that when one track is played after another there aren't any sudden jumps in volume. This means essentially that the loudness wars are over, because tracks that are mastered for maximum loudness will simply be played at a lower volume when streamed, so they will in fact sound quieter than more dynamic tracks that haven't been mastered for loudness.

So the best approach is to master your tracks to average -14 LUFS, while preserving the natural dynamic range of the music (-14 LUFS allows for a decent amount of dynamic range, especially compared to CD masters which may have only had 1 or 2 DB of dynamic variance throughout a track). Of all the options available only Pro L2 and Klevgrand Grand Finale have LUFS metering, but Grand Finale only offers momentary metering whereas Pro L2 can meter for the average of the whole song.

Thanks for this valuable info. I’m truly glad that the loudness wars are over. I hate over-compressed loud music. Guess I am still stuck in the CD era but am catching up to the new ways of doing things. Just converted from Pro Tools and am also learning to deal with the pluses and minuses of Auria. Thanks again.